aboutsummaryrefslogtreecommitdiff
path: root/2024/07-Bridge_Repair/first.hs
diff options
context:
space:
mode:
authorJulien Dessaux2024-12-07 13:56:28 +0100
committerJulien Dessaux2024-12-07 13:56:28 +0100
commit4c205242a592e022f28c7881e0f230db065b9cfc (patch)
tree4b018753318e1a5efe5b0c51cd764e24af47f23b /2024/07-Bridge_Repair/first.hs
parent2024-01 in factor (diff)
downloadadvent-of-code-4c205242a592e022f28c7881e0f230db065b9cfc.tar.gz
advent-of-code-4c205242a592e022f28c7881e0f230db065b9cfc.tar.bz2
advent-of-code-4c205242a592e022f28c7881e0f230db065b9cfc.zip
2024-07 in haskell
Diffstat (limited to '')
-rw-r--r--2024/07-Bridge_Repair/first.hs50
1 files changed, 50 insertions, 0 deletions
diff --git a/2024/07-Bridge_Repair/first.hs b/2024/07-Bridge_Repair/first.hs
new file mode 100644
index 0000000..ba85958
--- /dev/null
+++ b/2024/07-Bridge_Repair/first.hs
@@ -0,0 +1,50 @@
+-- requires cabal install --lib megaparsec parser-combinators heap vector
+module Main (main) where
+
+import Control.Applicative.Permutations
+import Control.Monad (void, when)
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+
+exampleExpectedOutput = 3749
+
+data Equation = Equation Int [Int] deriving Show
+type Input = [Equation]
+
+type Parser = Parsec Void String
+
+parseNumber :: Parser Int
+parseNumber = read <$> some digitChar <* optional hspace
+
+parseEquation :: Parser Equation
+parseEquation = Equation <$> parseNumber <* string ": "
+ <*> some parseNumber
+
+parseInput' :: Parser Input
+parseInput' = some (parseEquation <* eol) <* eof
+
+parseInput :: String -> IO Input
+parseInput filename = do
+ input <- readFile filename
+ case runParser parseInput' filename input of
+ Left bundle -> error $ errorBundlePretty bundle
+ Right input' -> return input'
+
+compute :: Input -> Int
+compute = sum . map total . filter valid
+ where
+ total (Equation t _) = t
+ valid (Equation total numbers) = elem total $ combinations numbers
+ combinations [x] = [x]
+ combinations l = let x = last l
+ xs = init l
+ in concatMap (\n -> [x+n, x*n]) $ combinations xs
+
+main :: IO ()
+main = do
+ example <- parseInput "example"
+ let exampleOutput = compute example
+ when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+ input <- parseInput "input"
+ print $ compute input